Prepping For Mold Making

Saturday and Sunday were all about prepping for mold making. As you saw in the last post, the surface was very good as evidenced by the reflections. In the video, you will see more reflections and even better ones from yesterday morning when I called it quits on contour sanding.

The majority of the time on Saturday was spent trying to fill pin holes. I did try using the Evercoat 400 pin hole filler again. As we learned Friday, it was too hot to apply the product. It kicked off and hardened almost immediately. This time I tried refrigerating the product to give me more time to work it into the pin holes. Again it kicked off immediately. Not going to work. I am sure it is a fine product, and if I were attempting this at 80 degrees I would try it again, but as of right now I can’t recommend the product until I see how it works in more reasonable temperatures.

That means that I was back to epoxy wiping for pin hole eradication. Basically, wipe epoxy over the surface and squeegee as much off as possible. Then repeat. Do this 3-5 times and the pin holes should be filled. In my temperatures, I was able to sand this about 3-4 hours later.

But low and behold, it didn’t fill all my pin holes. I am not sure if I didn’t put enough coats on or if the resin is too thin and runs out of the pin holes at this temperature. While the epoxy wipe certainly improved the surface, there was certainly more work to do.

Since sanding epoxy is not easy, I moved on to try the “Icing” glazing putty. This worked out great. So Kevin and I spread a very thin layer of glazing putty over the whole cowl. It took many small batches, but we got it covered. It was then another round of sanding and primer.

This time we nearly got all the pin holes. There are still some, but I am going to take care of those on the mold. Waxing the tooling cowl will fill some of the pin holes to some depth and further improve the surface. Secondly, it will be easier to do a quick sand with 400-800 grit on the mold surface to get rid of a small high spot than fill a pin hole.

Doing the icing of the whole tool cowl also had one more benefit. There turned out to be very shallow low spots on the whole tool cowl as you can see in the time lapse. All the blue splotches turned out to be fixed lows. Basically a two-for with doing the icing.

Saturday evening ended up being a late night finishing with spraying the tool cowl black. Sunday morning, then started with polishing the black primer. I was amazed how well it polished and how consistent the surface was. More and better reflections were evident in the black surface. We were ready to move on.

The tool cowl is currently proud of the surface of the fuselage. This happened because the tool cowl was originally meant to be a female mold. Therefore the inside surface of the tool cowl is actually where we want the outside surface to be. Since the drywall mud surface was not as good as I should have accomplished before attempting to mold, we decided to make that layup into a further refined plug. Therefore I needed to re-jig the tool cowl back flush with the fuselage.

So I took my mold release wedges out and started working them between the tool cowl and the plug, including my new favorite one. I recently purchased a mold release wedge that has a pneumatic fitting in it. This allows you to shoot compressed air in between your part and what you are releasing from (plug or mold). You can literally see your part “inflate” as it releases further and further. That was awesome to see.

It took about 15 minutes of careful work to get the tool cowl released from the plug. I was actually pleasantly surprised with the inside surface. Turns out my drywall compound surface would have been acceptable for the mold. But with the work we did on the tool cowl, we will get an even better and lighter part. I am still glad we did that.

I next removed the plug materials in all but the last 6-8 inches or so. I left this part of the plug there to allow easier jigging of the tool cowl. Between the cowl attachment flange marks on the forward cowl lip, and the aft part of the plug, this locates the tool cowl precisely back where it was.

From there I was able to trim the front edge of the tool cowl to be representative of what we want in the final part. Once I did that I was able to jig the cowl back into place. I drilled two number 40 holes for clecos in the extreme edge of the part to allow quick repeatable location. I then used popsicle sticks hot glued to the surface as my alignment for flush with the fuselage. These hot glue patches were put on top of tape to prevent marring my surface. The tool cowl was then affixed to this location and flush with the fuselage contours using dabs of hot glue between the cowl flange and inside surface of the tool cowl.

The rest of the day was spent applying and buffing 5 coats of mold release wax. I had to go in very small areas so the wax didn’t get too hard to buff.

By the time the evening rolled around, I was ready to apply PVA mold release. Three coats ought to do it. It is applied with a spray gun, and I tend to run it easily. To my surprise the first coat went off pretty well. Then I sprayed a second coat. Just as I finished my second coat, I heard it coming.

It is monsoon season here in Phoenix, and from time to time we get Haboobs, or dust storms. One was hitting the airport. I got the door closed in time, but unfortunately our hangars leak like sieves. The dust was flying around the hangar. Right into my wet PVA surface. Drat.

The nice thing about PVA is you can wash it off with water. So next, after I finish this post, I will run to the hangar to fix it. I will wash the PVA off with water. Dry the cowl. Put one more coat of wax on. Then re-PVA. No sense making a mold on a bad surface with all the work we did on the tool cowl. Hopefully I can get the mold laid up today.